Operating range advancement of a dual-inverter driven machine through voltage range enhancement

Speed range maximization of a traction drive is one of the main focus points in transportation electrification research. This paper presents a range improvement method, suitable for each type of open-winding three-phase electric machine. A dual-inverter drive system is proposed, which is capable of enhancing the phase voltages applied to the open-winding electrical machine. A common-mode current at the third-harmonic of the intended output frequency is deliberately generated to boost the supply voltage of one inverter, thereby extending the operating range of the machine above the base angular velocity. The need for a reactive fundamental frequency current to weaken the machine field is avoided as a result. A method is introduced for simultaneously optimizing the inverter voltages and minimizing the required boost current, thereby maximizing the speed range and the overall efficiency. The analysis is explained and verified by experiments. A relative angular velocity advancement of a factor 1.6 is achieved using voltage range enhancement.